Throwing fuel on the fire in the petrol versus diesel debate

When it comes to the used car market, I don’t pay much attention to the ‘official’ industry line on anything. Instead, I listen to you. And the burning question in the emails I’ve been getting lately is: “Should I buy diesel or petrol?”

This is an ongoing issue and won’t go away until there is an official answer via the fuel tax system. In the meantime, please let me make it clear that if you are buying a used car and don’t do that many miles - say, around 10,000 a year - then you might as well buy petrol.

Before I replied to a reader, I looked out of the window and noted that the four cars on my drive were all petrol, while the quite old one in the garage was also petrol-powered. I really don’t need diesel in my life and, depending on the circumstances, neither do you.

Now, I know that 85mpg is all very impressive, but you will have to spend a substantial amount of money to enjoy that level of fuel economy. Used cars don’t have to be dirt cheap, but the most singular appeal is that they dial out the most expensive motoring cost of all: depreciation.

The second biggest cost is fuel, unless you have a major engine breakdown, which will take you back to square one. So although you can get lucky with a high-mileage diesel, I get rather frightened by the associated particulate filters, turbos and dual-mass flywheel clutches, never mind all those injectors that have to be replaced.

Our reader wasn’t looking for anything complicated, either; he just wanted a sensible family car to do a solid few thousand miles each year without breaking down. His budget meant he was in the market for relatively recent 100,000-mile motors. So petrol it was.

The shortlist included a Vauxhall Insignia or a Honda Accord, and I unadventurously suggested a Ford Mondeo or Toyota Avensis. So with £5000 to spend - my projected average for a decent used buy - the options are a 40,000-mile 2009 Insignia 1.8 16V SE, a 2008 Accord 2.0i EX with 69,000 miles, a 60,000-mile 2008 Mondeo 2.0 Zetec or a 2009 Avensis 1.8 V-Matic TR with 74,000 miles.

The Avensis was interesting because it was the latest shape. And you can never rule out the Mondeo, which is consistently a lot of car for the money. However, the Insignia seemed to me like the pick of the bunch on sheer value.

Our reader, though, is poised to dive into an Accord - the most sensible thing to do. It’s not only classy but also shouldn’t give the owner any sleepless nights. In fact, none of those models should, and 99% of the reason for that is because they are run-in petrols. So buy them.

Join the debate

I only ever buy used motors, do modest mileages, and would never, ever consider a diesel. Notwithstanding reliability issues, my choice is also based on consideration for other road users and pollution concerns. Over the weekend I was stuck for 15 minutes or more in slow-moving traffic behind a 58-plate Audi A6 diesel. Every time he touched the accelerator (and that was often given the conditions) I was treated to an enveloping cloud of black smelly smoke, hindering vision and necessitating the closing of all my vents ... and I could still smell the bloody thing. Now this car was obviously unwell, but functioning, and I was annoyed at how one person could so affect fellow motorists (and nearby pedestrians/cyclists). Eventually, and thankfully, the traffic cleared and the Audi disappeared into the distance, dragging its pungent haze behind it. An extreme case, yes, but far from an isolated one in my experience. A used diesel? Not for me, thanks.

Good article. I was trying to explain this to a friend who does 10k miles a year. He was adamant that a diesel car would be cheaper as it would depreciate less, despite its extra complexity. He got a second hand Ford Focus 1.6 diesel with 55k miles on the clock. 5k miles in, his turbo failed taking out the whole engine with it. A secondhand engine cost 2k. Despite this he thinks he was unlucky and that diesels are still cheaper to run. Now he wants to get a second hand A4 2.0 diesel with 60k miles on the clock, his reasoning being that Audi engines are more reliable than Ford ones. By this time I had already given up.

...He got a second hand Ford Focus 1.6 diesel with 55k miles on the clock. 5k miles in, his turbo failed taking out the whole engine with it. A secondhand engine cost 2k...

This is precisely what happened to my Ford Focus (mine a 1.8 diesel). As at he time I was only doing 5k miles year, mostly short journeys, the engine often did not warm up properly and sure enough after a time the turbo went.

Next car is definitely going to be a petrol and that's the advice I'd give to anyone else, unless they need to high motorway miles daily.

" Now he wants to get a second hand A4 2.0 diesel with 60k miles on the clock, his reasoning being that Audi engines are more reliable than Ford ones. By this time I had already given up."

Now that is something, he clearly doesn't learn. Aren't those the engines where the balancer shaft works loose and kills the engine? Frying pan -> fire.

Personally, I have a diesel despite only doing infrequent long runs - I need it for pulling the caravan. That said, I keep looking for reasonable ways I could use petrol power for the same job. Even better than regular petrol, would be a Toyota Hybrid - the Prius we also have is indestructible and gives decent economy. So, a Lexus 450h is on my shopping list, just need to save up a bit...

Winnie, I'm on your side of the argument but in your friend's case it may not have been the diesel so much as the make. I had a 2001 Mondeo 2.0 petrol which spat its oil out on the M6 causing a total seizure of the engine. The only diesel I've owned was a Rover 600, which I ran for a couple of years. It served me faultlessly apart from a couple of times the diesel froze (waxed?) in the severe Highland winters. That was a 1997 car so maybe newer ones have something built in to prevent the problem. I would still be in no rush to go for diesel again, though, as the engine was the weakest point of that Rover, purely because of the lack of refinement, contrary to the overall character of the car. It went well but it was noisy compared to petrol engines, and noisy in a rough way at that. I don't do the very high mileage I used to, but even looking back with hindsight I wouldn't change any of the petrol cars I've owned for a diesel version.

Petrol all the way for me. I only do 10k miles a year but id stick with petrol even if i did more miles.
My IS250 will do low 40 mpg on a sensible law abiding motorway run. The extra MPG of a diesel has to compensate for higher fuel prices, higher servicing costs, higher purchase price before I turn a "profit" on a diesel choice. And then youd still be left with more reliability worries and less refienment. I used to commute 100 miles a day. My car of choice? A civic type R. An Passat TDi would simply have not done. Sure better MPG would have benefited my wallet - but i enjoyed every single second of driving the type R. A diesel saloon would have been nothing more than an appliance after a while. In short, I got more value out of the money spent owning and running the type R than a diesel commute car. Priceless.

I worked through this argument earlier this year and ended up with a 1.8 petrol Civic. Whilst I have some reservations about certain aspects of the car, I have no doubt that my decision to go for petrol was the right one, even though I do around 12k a year. Plus, as this debate shows no signs of going away, I suspect my petrol Civic will be quite desirable on the used market when I come to sell it. But, the debate isn't as simple as petrol v diesel - some petrols, like Ford's 1.0 ecoboost in 125ps guise, have dual-mass flywheels as well as turbos and high pressure injection so there is a notable risk of a big bill above 100k miles.

At one of my oft-used filling stations, diesel, is currently 114.9p, which is 1p cheaper than their petrol! I have not bought second hand diesel and quite possibly would not either. I would likely take James's advice! However, I do like the feel of diesel torque. I tried the petrol 1.4ACT in a Golf, but preferred the diesel which won the day for me on a new purchase. Mpg is not the only criteria. I too object to following a poorly running diesel, but if servicing and the MOT is being done properly, how are these still on the road? There is no belching smoke from diesels with particulate filters. The particulate filters do eventually fill up with 'ash' matter that cannot be burned out/expelled, so would have to be replaced, but that could well be at some point beyond 100k miles. However, the catalytic converters in petrol can be damaged at any time by misuse (e.g. driving through flood waters/sudden cooling, or bump-starting the car/neat petrol contaminates them) and I would expect are costly to replace come MOT time when the car fails to pass.

In your piece you also mentioned potential headaches with turbos. Thanks to the downsizing trend foisted upon us by various governments these things are becoming more-prevalentin petrol motors, too. It wouldn't be bad if replacing them was an couple hours of labor and a part that only cost 100 quid but usually these things cost well over a grand and labor on them are astounding. That is why I am avoiding turbocharged cars like the plague but they are getting harder to find.